hmmm i guess in MVs like wanna, well to show that the girls are having fun and are good friends, you know how friends always hang out in their friend's room when their in his/her home, thats why maybe the girls in the MVs are always in a room setting, and thus the bed.
in MVs like honey, i guess when you're emoing or sad you are probably alone in your own room, and hence a room setting with just the one person in it to express the loneliness, and thus the bed as well.
As for Lupin and jumping, hmmm i guess...beds are cool? might as well.